As the parts for outer panels of cars and household electric appliances and the like, shaped articles of polyolefin of which constituent unit is an olefin such as ethylene, propylene and the like are widely used in place of metals. These shaped articles are frequently coated with two-package type top paint containing polyisocyanate compound, and in such occasions, usually chlorinated polyolefin-containing primer is applied in advance, for improving adherability between the top coating film and the shaped articles.
Conventionally, a rubber component (e.g., styrene butadiene rubber, isoprene rubber and the like) was added to polyolefin shaped articles, for improving adherability or impact resistance. In recent years, however, addition of such rubber component has been quantitatively reduced or entirely stopped, which gave rise to a problem of deterioration in adherability of conventional primer with such shaped articles.
With the view to solve this problem, the present applicant previously proposed a primer which used specific chlorinated polyolefin and blocked polyisocyanate concurrently with polyol resin (cf. JP 2002-121462A). For this primer, aromatic organic solvent such as toluene or xylene is used to secure solubility of the chlorinated polyolefin, but conversion to water-borne compositions is required also for primer from the viewpoints of sanitary safety and environmental preservation.
Various attempts are made to prepare aqueous dispersions of chlorinated polyolefin, to meet the above demand (e.g., see JP 2003-327761A, JP 2004-91559A).
In recent years, furthermore, polyolefin shaped articles are given increasingly higher rigidity and satisfactory adherability thereto of coating films cannot be obtained from aqueous dispersions of chlorinated polyolefin heretofore used for primer, particularly under such low temperature baking conditions as around 80-90° C., posing another problem difficult to cope with. Still in addition, in the use for car parts, primer concurrently having gasohol resistance is now in demand. Thus, it is becoming even more difficult to effectively meet all of these demands.